NAME
Judy - Library for creating and accessing dynamic arrays
DESCRIPTION
The Judy family of functions supports fully dynamic arrays. These arrays
may be indexed by a 32- or 64-bit word (depending on processor word
size) (Judy::1, Judy::L), a null terminated string (Judy::SL), or an
ordinary perl string (Judy::HS).
Judy arrays are both speed- and memory-efficient, with no tuning or
configuration required, across a wide range of key set types
(sequential, periodic, clustered, random). Judy's speed and memory usage
are typically better than other data storage models such as skiplists,
linked lists, binary, ternary, b-trees, or even hashing, and improves
with very large data sets.
The memory used by a Judy array is nearly proportional to the population
(number of elements).
Since an initial (empty) Judy array is represented by a null pointer, it
is possible to construct an array of Judy arrays. In other words, a Judy
array's Values can be pointers to other Judy arrays. This makes it very
simple to construct an array with an arbitrary number of dimensions or
Index sizes.
The libJudy author believes JudyHS is a good replacement for a hashing
method when resizing the hash table is done during population growth. A
correctly tuned hash method with a static hash table size and population
is unbeatable for speed. However, Judy::HS will perform better than a
hashing method with smaller and larger populations than the optimum hash
table size. JudyHS does not have a degenerate performance case where
knowledge of the hash algorithm can be exploited. (I.E. JudyHS does not
use a linked list to handle hash collisions, it uses a tree of JudyL
arrays and a virtual hash table size of 4 billion).
SYNOPSIS
Judy::1:
This can be thought of as a bit vector. For a comparison between
Judy::1 and "vec" in perlfunc, take a look at
.
# Turn the 43rd bit on. A bit like:
#
# vec( $str, 42, 1 ) = 1
#
Judy::1::Set(
$judy_1,
42
);
Judy::L
Maps an integer to another integer. This is sort of like a very
compact perl hash where the only allowed keys and values are
integers.
# A bit like:
#
# $array[ 42 ] = 9000
#
Judy::L::Set(
$judy_l,
42,
9000
);
Judy::SL
Maps null terminated strings to integers.
# A bit like:
#
# $hash{world} = 9000
#
Judy::SL::Set(
$judy_sl,
'world',
9000
);
Judy::HS
Maps perl strings to integers.
# A bit like:
#
# $hash{world} = 9000
#
Judy::HS::Set(
$judy_sl,
'world',
9000
);
Multi-dimensional Judy::L/Judy::SL/Judy::HS Arrays
Storing a pointer to another Judy::L array in a Judy::L array's Value is
a simple way to support dynamic multi-dimensional Judy::L arrays. These
arrays (or trees) built using Judy::L arrays are very fast and memory
efficient. (In fact, that is how JudySL and JudyHS are implemented). An
arbitrary number of dimensions can be realized this way. To terminate
the number of dimensions (or tree), the Value pointer is marked to NOT
point to another Judy array. A "Judy::JLAP_INVALID" flag is used in the
least significant bit(s) of the pointer. After the flag
"Judy::JLAP_INVALID" is removed, it is used as a pointer to the users
data.
Note: The current version of Judy.h changed this flag from 0x4 to 0x1 to
allow for a malloc() that does not deliver memory on an 8 byte aligned
boundry (such as old v algrind).
The following example code segment can be used to dive into a
multi-dimensional Judy::L using an API similar to Tye McQueen's
Data::Diver. This makes a Judy::HS object and looks past the public API
as an example of a multi-dimensional Judy::* structure.
# For kicks, allocate a Judy::HS object and look inside it a
# little bit.
use Judy::HS;
Judy::HS::Set( my ($judy), 'abcd', 42 );
Dive( $judy, 4 );
use Judy;
use Judy::L;
sub Dive {
my ( $judy, @walk ) = @_;
my ( $pvalue, $value );
for my $key ( @walk ) {
return if ! $judy;
# Advance to next dimension.
( $pvalue, $value ) = Judy::L::Get( $judy, $key );
# Check if pointer to user buffer
last if $value & Judy::JLAP_INVALID;
$judy = $value;
}
if ( $value & JLAP_INVALID ) {
# Remove our flag.
$value &= ~ Judy::JLAP_INVALID;
# Return the value.
printf "User object pointer is 0x%x at 0x%x\n", $value, $pvalue;
}
else {
warn sprintf "Judy::* object pointer is 0x%x at 0x%x\n", $value, $pvalue;
}
return ( $pvalue, $value );
}
Note: This works because malloc() guarantees to return a pointer with
the least bit(s) == 0x0. You must remove JLAP_INVALID before using the
pointer.
CONSTANTS
JLAP_INVALID
PJERR
SEE ALSO
- the C library home page
Judy::1 - maps an integer to a bit
Judy::L - maps an integer to an integer/pointer
Judy::SL - maps a null terminated string to an integer/pointer
Judy::HS - maps a string to an integer/pointer
A 10 MINUTE TECHNICAL DESCRIPTION may be found at
A 3 HOUR TECHNICAL DESCRIPTION (out of date and a bit corny) may be
found at
FILES
Locations of interest include: http://sourceforge.net/projects/judy --
project downloads file:/usr/share/doc/Judy/ -- for HTML version of man
pages. /usr/share/doc/Judy/demo/ -- demonstration program source files.
The author attempted to write interesting application notes using
advanced features of Judy. They may be found at
"http://judy.sourceforge.net/application/ (Some may be out of date).
ERRORS & WARNINGS
File '%s', line %d: %s(), JU_ERRNO_* == %d, ID == %d
See the header file Judy.h from the Judy C source library. You
already have a local copy of this to have been able to build this
perl library.
Sorry, can't use keys longer than %d for now. This is a bug.
Coercing %d to 0. Can't use negative values as keys.
Truncating %d to %d because your number is larger than fits in a signed
integer
Truncating %d to %u because your number is larger than fits in an
unsigned integer
Truncating %d to %d because your number is smaller than fits in a signed
integer
Dropping UTF8 flag for '%s'
BUGS
Please report any bugs or feature requests to "bug-Judy-HS at
rt.cpan.org", or through the web interface at
. I will be
notified, and then you'll automatically be notified of progress on your
bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc Judy
You can also look for information at:
* RT: CPAN's request tracker
* AnnoCPAN: Annotated CPAN documentation
* CPAN Ratings
* Search CPAN
ACKNOWLEDGEMENTS
Doug Baskins, totally.
Michael Schwern for writing Alien::SVN which made this possible.
Tye McQueen for inspiring the minimal API.
Yitzchak Scott-Thoennes for reminding me that perl's magic requires
extra care and attention.
COPYRIGHT & LICENSE
Copyright 2012 Josh Jore, all rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
SOURCE AVAILABILITY
This source is in Github:
AUTHOR
Judy was invented by Doug Baskins (dougbaskins .AT, yahoo.com) and
implemented by Hewlett-Packard. (Note: Judy is named for the inventor's
sister, after discarding many proposed names.)
The perl wrapper was written by Josh Jore